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EDD66 is the preferred index used to produce daily gas demand forecast for gas system operations. EDD66 indicates three-hourly observations between 6am of the current calendar day to 6am of the following calendar day. EDD66 is also known as dfs_edd publish in the MIBB report.
The EDD66 formula is shown in the table below
EDD66 = Temperature Degree Day (DD66) Wind chill
0.038 * DD66 * 0.604 * Wind66
0.18 * Sunshine hours
2 * Cosine (2*PI*(day – 200)/365)
Temperature T66: This is the average of the eight three-hourly Melbourne temperature readings (in degree Celsius) from 6am to 6am the following day inclusive as measured at the Bureau of Meteorology’s Melbourne Station. A 50% weighting is applied to the 6am temperature observation.
The Degree Day (DD) DD66 = 18 – T66 if T66 < 18
= 0 if T66 is greater than or equal to18
T66 = ((T6AM + T6AM (NEXT GAS DAY))/2 + T9AM + T12PM + T3PM + T6PM + T9PM + T12AM + T3AM) / 8
18 degrees C represents the threshold temperature for residential gas heating – this threshold (of about 65 degrees F) is a fairly common standard internationally.
Average Wind66: This is the average of the eight three-hourly wind observations (measured in knots) from 6am to 6am the following day inclusive measured at the Laverton and Moorabbin Stations. A 50% weighting is applied to the 6am wind observation.
A localisation factor is applied to account for the shift from the Melbourne wind station (closed in 1999) to the average of Laverton and Moorabbin wind stations in order to align them with the Melbourne wind station reading. This factor is highlighted in red.
Wind66 = ((W6AM + W6AM(NEXT GAS DAY))/2 + W9AM + W12PM + W3PM + W6PM + W9PM + W12AM + W3AM ) / 8
Sunshine Hours: This is the number of hours of sunshine above a standard intensity as measured at the Weather Bureau’s Tullamarine Station.
Seasonal Factor (COSINE function): This factor models seasonality in consumer response to different weather. It indicates that residential consumers more readily turn on, adjust heaters higher or leave heaters on longer in winter than in the shoulder seasons for the same weather or change in weather conditions. For example, central heaters are often programmed once cold weather sets in resulting in more regular use. This change in consumers’ behaviour is captured in the Cosine term in the EDD formula, which implies that for the same weather conditions heating demand is higher in winter than in the shoulder seasons or in summer.